FIG. 1 shows a typical inkjet printer 10 that emits droplets of ink onto print media 12, such as paper, to create images and text. Inkjet printer 10 includes a printhead (not shown) mounted within a carriage 14 that travels back and forth across the print media 12. The printhead includes an array of tiny nozzles that emit the droplets of ink. As the printhead is moved across the print media 12, a controller activates the printhead to emit droplets of ink at precise locations corresponding to a pattern of pixels of the image being printed.
Ink is typically provided to the printhead by an ink cartridge 16 that is attached to the carriage 14. Depending on the design of the printer 10, the ink cartridge 16 can come in various combinations ranging from a single cartridge for black ink to multiple cartridges for each desired ink color. The ink cartridge 16 may even include the printhead itself. In addition, the ink cartridge 16 may be stationary and separate from the carriage 14.
Different types of inkjet printers emit the droplets of ink in different ways. The two main inkjet technologies currently used by printer manufacturers are thermal bubble and piezoelectric. The thermal bubble method (also known as bubble jet) is used by manufacturers such as Canon and Hewlett Packard. FIG. 2A shows a typical bubble jet printhead 20 used in a thermal inkjet printer. In printhead 20, a heating element 22 such as a resistor creates heat that vaporizes ink in a reservoir 24 to create a bubble. As the bubble expands, a tiny amount of the ink is pushed out of a nozzle 26 onto the paper. When the bubble collapses, a vacuum is created that pulls more ink into the reservoir 24 from the ink cartridge 16 (FIG. 1).
FIG. 2B shows a typical piezoelectric printhead 30 used in a piezoelectric inkjet printer by manufacturers such as Epson. In printhead 30, a transducer 32 such as a piezo crystal is located at the back of an ink reservoir 34. The transducer 32 receives an electric signal that causes it to vibrate. When the transducer 32 vibrates inward toward the reservoir 34, it forces a tiny amount of ink out of a nozzle 36 onto the paper. When the transducer 32 vibrates outward away from the reservoir 34, it pulls more ink into the reservoir 34 from the ink cartridge 16.
Inkjet printers have several advantages when compared to other types of printers, and as a result, inkjet printers have become increasingly popular. First, inkjet printers are capable of very high resolutions. Current inkjet printers can emit droplets of ink as small as 2 picoliters. This allows the printhead to produce images with resolutions exceeding 4800 dots per inch (dpi). Also, because the printhead never actually touches the paper when creating an image, inkjet printers are very quiet during operation. Similarly, because the printhead never touches the paper, inkjet printers are very versatile in that they can print on a wide variety of print media. Finally, inkjet printers are affordable to purchase, and affordable to operate. The ink cartridges they use are cheap, easy to replace, and readily available.
Inkjet printers do, however, have certain limitations. Because inkjet printers are non-impact printers, they are not capable of printing through multi-page print media such as carbon copy forms. Multi-page print media is commonly used in many types of recordkeeping, including accounting bills, invoices, and so on, and in any industry where a duplicate or “carbon copy” is required. Typically, in order to print on multi-page print media, an impact printer such as a dot matrix printer is used. This is because an impact printer is needed to exert sufficient force to the media to transfer the printed images and text to underlying layers of the media. A typical dot matrix printer strikes pins or hammers against an ink ribbon to produce dots on the print media. The pins are housed within a printhead, and a carriage moves both the printhead and the ink ribbon back and forth across the print media. Images and text are created by appropriately positioning numerous individual dots on the print media. As the pins strike a top layer of the multi-page print media, the force of the pins also cause corresponding dots to be printed on underlying layers of the print media. As will be understood by those skilled in the art, where the multi-page print media is carbon paper there are thin pages coated with a waxy pigmented coating placed between sheets of paper. The pressure of the pins striking an upper sheet of paper causes transfer of the pigment to a lower sheet of paper.
FIG. 3 shows a typical printhead 40 used in a dot matrix printer. The printhead 40 includes an array of individual pins 42. The number and arrangement of the pins determine, in part, the resolution of the printed images and text. Current dot matrix printheads typically contain between 9 and 24 pins. However, there are several disadvantages to using dot matrix printers. First, the print quality is relatively poor because the spacing between the pins in the printhead typically determines the spacing between the printed dots. Even when the printhead contains 24 pins the quality is noticeably inferior to inkjet printers. Also, dot matrix printers require special paper to be printed on. Typically, dot matrix printers use tractor-feed continuous paper, where the pages are continuously connected and have holes along both vertical edges. This type of paper has horizontal perforations between the pages so that the pages and vertical edge portions including the holes can be separated after the printing process is completed. Not only is this type of paper expensive and plagued with alignment issues (the holes must be aligned properly for the printer to function properly), but if the user desired to print on carbon copy paper, then the carbon copy paper necessarily has to be restricted to only the tractor-feed continuous type paper. And finally, dot matrix printers are notorious for being noisy during operation.
There is a need for printing high quality documents and for creating duplicate copies of such documents during printing.